A CDF uses a filtering technique of a switched-capacitor network (SCN). The SCN is a common circuit in discrete time signal processing and includes a plurality of switches and a plurality of capacitors. By turning on and off the switches, the CDF could control the state of charge storage of the capacitors so as to filter an input signal. Compared to a capacitive resistive analog filter circuit, the filtering effect of the SCN is mainly decided according to the size ratio between the capacitors therein. Even if the process is altered to change the area of each capacitor, since the size ratio between the capacitors does not change with the process, the filtering effect of the SCN remains unchanged. Therefore, the SCN is suitable to be fabricated in a chip.
However, the average CDF decimates and samples the signal, and therefore a folding noise may be generated, thereby reducing system performance. Moreover, the average CDF generally does not use a bandwidth compensation circuit. As a result, the bandwidth thereof may be narrower, causing sinc-function distortion.